HAPPY COUPLES: Fred Couples, mostly free of the chronic back pain that had plagued him, tees off on the 12th hole yesterday at Westchester CC, where he held on to a one-stroke lead heading into the final round of the Senior Players Championship. Photo: Getty Images

After ages of agony, Fred Couples today can parlay his victory over chronic back pain into triumph on the course again.

Couples brings a one-shot lead over John Cook and Peter Senior into today’s final round of the Senior Players Championship at Westchester CC. The field will attempt to beat threatening weather by starting from the first and 10th tees between 8 a.m. and 10 a.m.

Couples says if his back pain returns, he will head back to Germany for another nontraditional blood augmenting procedure, and it would be hard to argue against it. Six weeks after his treatment, Couples stands 11-under in seeking his first victory of the year.

The treatment is not approved in the U.S., but Couples cleared it with the Tour’s anti-doping officials.

During the procedure, blood is taken from the patient’s arm and miniscule glass beads force the white blood cells to overproduce the desired protective and regenerative proteins. The resulting serum is separated from other blood components by centrifuge and injected into the affected area over the course of several sessions — six in Couples’ case.

“If I hadn’t gone to Germany, I wouldn’t be playing. I’d be waiting for it to thaw, and I don’t think it would,” Couples said this week. “That was my last hurrah, I guess, of giving something a shot. This is the last [doctor] I’m planning on going to see.”

Starting the day with a one-shot lead, Couples was caught momentarily by Senior on their opening hole. Couples then birdied Nos. 5, 7 and 9, and parred out the back nine while Senior had three birdies and a bogey on the back. Both Cook, who shot 5-under 66 yesterday, and Senior birdied No. 18 to pull within a shot of Couples.

“A good round, not great,” Couples said. “I’m still in the lead, but I’ll have to have a better round [today], I’m sure, to win.”

Couples won four times last year, his first on the Senior circuit after 15 triumphs on the regular tour. Pain limited his play to four tourneys this year before going to Germany, and this week’s Senior major is his second since. He finished tied for 26th at the 3M two weeks ago.

“I’ve done nothing all year, so [today] is a big day just to get back and win a tournament,” Couples said.

Couples said he won’t be happy just to contend.

“I’m either going to win or I’m not,” Couples said. “I’m not telling you second is bad. It’s irrelevant. This has been an odd year and I have a shot at winning.”

With the discomfort in his back at bay, Couples has a second lease on a career that otherwise might have been ending. There would be nothing routine about victory for him.